Strange EXT4 error, files doubled and trebled

Dear Sirs,
I DLed the trial version of your ETXfs driver on my Mountain Lion iMac.
Connected a WD Elements 2TB External USB disk to it and formatted it EXT4.
I then copied files from the Mac to the USB disk and later connected the USB disk to a Raspberry running the Raspbmc (debian derived) distro.

I now have around one third of the files which are TRIPLICATED and around another third of them appear TWICE.

What I mean is that if I do an ls of the files I see 2 or 3 IDENTICAL entries with the same name and same contents. This is true for both files and directories.

If I do an fsck under Linux the FS appears "clean".

If I do a disk check under Mac OS it finds corruption and fixes things but after some more time of usage the double and triple files appear again.

I do not know how to fix this since I am pretty sure that if I delete one "copy" I will in fact delete them all and lose the files.

Copying the contents on another disk will be hard since it's around 750 GB of data.

Any ideas please ? Thanks in advance.